NOTE: As their name suggests hints are not exactly WWE SmackDown! vs. RAW 2008 cheats, and are usually just simple (but very useful) tips on how you can unlock secret level, features, find hidden areas and such. Hopefully these will make playing WWE SmackDown! vs. RAW 2008 even more entertaining.

Achievements
Complete the following achievements to unlock Xbox Live Gamerscore points.

That's Gonna Leave A Mark (20 points): Powerbomb an opponent on top of a steel step in any match type.
Possession is 9/10 Of The Law (20 points): Steal your opponent's taunt 3 times in any One on One match.
Put'em In A Body Bag (20 points): Turn your opponent's entire limb damage meter red in any match type.
I'd Like To Thank The Academy (20 points): Defeat a Powerhouse Superstar with the Possum Pin in any match type.
You've Got A Bit Of Red On You (20 points): Get busted open by your opponent on legend difficulty in any match type and win.
Who Says Originality Is Dead (20 points): Create an original CAS, ring entrance and created Championship.
King Of The Mountain (20 points): Place first in every type of tournament in Tournament mode.
If It Bleeds... (20 points): Bloody every ECW Superstar on the roster.
Submission-Sensei (50 points): Win a Normal Submission match without having your Struggle Submission hold broken once.
Stop Yapping And Fight (20 points): Argue with the referee 4 times in a match and win.
That's One For The Record Books (20 points): Eliminate 20 opponents in a 30-Man Royal Rumble.
Now That's Hardcore (20 points): Bloody and defeat a Hardcore Superstar on legend difficulty in an ECW Extreme Rules match and win.
The Best There Was... (20 points): Win a 20-minute Ironman match on legend difficulty without surrendering a point to your opponent.
A Fighting Champion (75 points): In ranked online matches, defend a CAC title 5 times against 5 different players within 24 hours.
Gold Digger (70 points): Win a Created Championship 10 times in ranked online matches.
On Fire (75 points): Win 30 consecutive ranked online matches.

Additionally there are ten secret achievements.

Escape Artist (20 points): Wiggle free from every Ultimate Control Grapple at least once.
What The... (10 points): Preview the Mexican Stretch Turnbuckle move in Create a Moveset.
You've Got Guts (20 points): Complete a ranked online title match.
Send'em Back To Louisville (10 points): Lose to an opponent who has more limb damage than you.
Now Offering Non-Stop Flights (20 points): Stand on a ladder and suplex your opponent out of the ring in a ladder match.
Rope A Dope (20 points): Perform a succesful springboard attack off each side of the ropes.
This Year's Inductee (350 points): Play as a GM in 24/7 Mode and obtain the GM of the Year Award.
On The Job (10 points): Lose 5 consecutive ranked online matches.
Better Luck Next Year (10 points): Be the first Superstar eliminated in a 30-Man Royal Rumble.
This Is Coming Out Of Your Check (20 points): Break 15 tables and 10 chairs in a TLC match.

Main event mode unlckables
In main event mode, do the following things to unlock extra outfits and characters.

Unlockable Characters
JBL: Gain Main Eventer ranking in Main Event mode for the SmackDown brand
Shane McMahon: Gain Main Eventer ranking in Main Event mode for the Raw brand
Vince McMahon: Gain Main Eventer ranking in Main Event mode for the ECW brand